javascript $getJSON 和 for 循环问题
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$getJSON and for loop issue
提问by Onei
This is to populate a table with the amount of results that are returned from the MediaWiki API query /api.php?action=query&list=querypage&qppage=BrokenRedirects. The number of results is then added to the id, for example:
这是用从 MediaWiki API 查询返回的结果数量填充表/api.php?action=query&list=querypage&qppage=BrokenRedirects。然后将结果数添加到 id 中，例如：
// BrokenRedirects
$.getJSON('/api.php?action=query&list=querypage&qppage=BrokenRedirects&format=json', function (data) {
$('#BrokenRedirects').text(data.query.querypage.results.length);
});
But as it's being repeated another 7 times I made the arguments for qppage into an array and used a for loop to shorten overall code.
但是当它再重复 7 次时，我将 qppage 的参数放入一个数组中，并使用 for 循环来缩短整体代码。
var array = ['BrokenRedirects',
'DoubleRedirects',
'Unusedcategories',
'Unusedimages',
'Wantedcategories',
'Wantedfiles',
'Wantedpages',
'Wantedtemplates'];
for (var i = 0; i < array.length; i++) {
$.getJSON('/api.php?action=query&list=querypage&qppage=' + array[i] + '&format=json', function (data) {
$('#' + array[i]).text(data.query.querypage.results.length);
});
}
The first, unlooped, version works. But when I added a loop it didn't. The $getJSONpart executes, but it then fails to add the resultant data to the id. I ran it through JSLint which apart from complaining about functions in a loop and declaring var iwith var arrayreturned little help. I'm relatively inexperienced with javascript so thought perhaps a variable can't be used twice within a loop? Other than that, maybe something to do with using an id within a loop?
第一个未循环的版本有效。但是当我添加一个循环时它没有。该$getJSON部分执行，但随后无法将结果数据添加到 id。我跑了它通过的JSLint其中除了抱怨在一个循环的功能，并宣布var i与var array返回的帮助不大。我对 javascript 相对缺乏经验，所以认为一个变量可能不能在循环中使用两次？除此之外，也许与在循环中使用 id 有关？
回答by Denys Séguret
That's a classical problem : ihas the value of end of loop when the callback is called.
这是一个经典问题：i调用回调时具有循环结束的值。
You can fix it like this :
你可以像这样修复它：
for (var i = 0; i < array.length; i++) {
(function(i) { // protects i in an immediately called function
$.getJSON('/api.php?action=query&list=querypage&qppage=' + array[i] + '&format=json', function (data) {
$('#' + array[i]).text(data.query.querypage.results.length);
});
})(i);
}
2018 addendum:
2018 年附录：
There's now another cleaner solution in today's browsers: use letinstead of var:
在当今的浏览器中，现在有另一种更简洁的解决方案：使用let代替var：
for (let i = 0; i < array.length; i++) {
$.getJSON('/api.php?action=query&list=querypage&qppage=' + array[i] + '&format=json', function (data) {
$('#' + array[i]).text(data.query.querypage.results.length);
});
}
回答by Girish
getJSON is an asynchronousajax call
getJSON 是一个异步ajax 调用
REFER: use synchronous ajax calls
REFER：使用同步ajax调用
回答by user2973469
Use Jquery $.each()to iterate over the array instead of a for loop.
使用 Jquery $.each()迭代数组而不是 for 循环。
For example:
例如：
$.each(array, function(_, value) {
var url = '/api.php?action=query&list=querypage&qppage=' + value + '&format=json';
$.getJSON(url, function (data) {
$('#' + value).text(data.query.querypage.results.length);
});
});
回答by Piyas De
You should write a function like -
你应该写一个函数，比如 -
function callUrl(value)
{
$.getJSON('/api.php?action=query&list=querypage&qppage=' + value + '&format=json', function (data) {
$('#' + value).text(data.query.querypage.results.length);
});
}
and then call it with some timeout option like -
然后使用一些超时选项调用它，例如 -
setTimeout('callUrl(+ array[i] +)',500);within the loop -
setTimeout('callUrl(+ array[i] +)',500);在循环内 -
i.e.
IE
for (var i = 0; i < array.length; i++) {
setTimeout('callUrl(+ array[i] +)',500);
}
Some delay for each call will be required here.
此处需要对每个呼叫进行一些延迟。
